This invention generally relates to gas-to-gas heat exchangers, and more particularly to modifying airflow through regenerator cores of a gas-to-gas heat exchanger.
Heat exchangers can significantly improve the efficiency of many energy conversion devices by capturing waste heat from the exhaust stream of an energy conversion process and transferring the captured heat into the input stream of the energy conversion process. Capturing and using waste heat from the conversion process exhaust stream reduces the amount of energy used by the energy conversion device, which improves energy conversion device efficiency. For example, heat exchangers may improve the efficiency of gas turbine engines, fuel cells, regenerative thermal oxidizers or other combustion devices. As another example, a heat exchanger recovers waste heat from a gas turbine engine exhaust, reducing the amount of fuel used to achieve a given combustor exit temperature and improving the thermal efficiency of the gas turbine engine.
Conventional heat exchanger designs use stationary counter-flow fin-and-plate recuperators or rotating ceramic matrix regenerator heat exchangers. Stationary counter-flow heat exchangers pass heated turbine exhaust through a series of plates separating the heated exhaust flow from the relatively cool compressor exit flow. The waste heat from the turbine exhaust is transferred from the high temperature exhaust stream to the cooler compressor exit flow. Typically, each plate includes fins to increase the heat exchanger effectiveness while reducing its size. However, the high-temperature materials needed for the stationary counter-flow recuperator and its relatively complex geometry limits its performance and adds significant cost to an energy conversion device. For example, in a microturbine gas turbine system, a recuperator has the largest cost component, often up to 30%, at is also physically large and complex to design and manufacture. The use of hundreds of small channels, generally from 1 to 5 millimeters, to provide sufficient flow area for heat transfer from hot flow to cold flow at minimal pressure drop causes much of this design complexity. Additionally, the channels are sealed and must be capable of sustaining a pressure and temperature difference between hot and cold sides. Hence, various parts and operations are used for recuperator construction, resulting in high costs that are difficult to significantly reduce, even with higher production volumes.
Rotating ceramic matrix heat exchangers include materials enabling high cycle temperatures and enabling high heat exchange effectiveness. However, leakage between a hot flow and a cold flow can cause significant loss, as 4% to 14% of the flow from the compressor may leak into a turbine, or other energy conversion device, exhaust. Additionally, a more complex system or gears and seals are needed to enable heat exchanger rotation. One type of rotating ceramic heat exchanger uses indexed rotation to disengage a movable seal from the face of the regenerator and move a rotor through a partial revolution before reengaging the seal. While this disengagement may reduce leakage by reducing seal wear, the components of such a heat exchanger are specialized, increasing heat exchanger cost.